Thermoplastic article having a metallic flake appearance

ABSTRACT

The transparent articles described herein have interspersed small particles with a metallic glint. This appearance is achieved by dispersing metal oxide-coated glass platelets within a thermoplastic matrix. It is desirable to take steps to avoid breaking the glass platelets during the process of preparing these materials.

CROSS REFERENCE TO RELATED PATENTS

None

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

This application relates to a transparent article having a metallicflake appearance. Specifically, this application relates to an articlethat comprises a pigment having a metallic flake appearance dispersedwithin a transparent thermoplastic matrix.

As thermoplastics become increasingly important in the marketplace,producers have sought to differentiate their products by making themmore visually exciting to the customer. One desirable look forthermoplastics is the metal flake appearance. This appearance can bedescribed as the look one could imagine if small pieces of metal weredispersed in molten glass, and the glass was subsequently cooled. Theflakes have a metallic glint, but one perceives clear spaces between themetallic flakes such that portions of the article are completelytransparent.

Until now, it has been very difficult to produce a thermoplastic articlehaving a metal flake appearance. Metal flakes, most typically aluminumflake, have been dispersed in thermoplastics to create a metal flakeappearance, but there are several disadvantages to this method.Specifically, the metal flakes tend to cause degradation of the polymer,which leads to a loss in mechanical properties. For instance, dispersingaluminum flake in polycarbonate will significantly decrease the impactstrength of the polycarbonate. Moreover, aluminum flake is hazardousbecause it can cause dust explosions. If aluminum flake does burn in afire, it burns at a very high temperature, which makes the fire verydifficult to extinguish.

Mica has also been dispersed in thermoplastics in an attempt to create ametallic flake appearance. Mica can provide a metallic flake appearance,especially when coated with a layer of an inorganic pigment such astitanium dioxide. However, mica has several drawbacks. Specifically,incorporating mica in a transparent thermoplastic tends to decrease thetransparency of the thermoplastic, producing a “milky” appearance. Micaalso degrades the physical properties of the thermoplastic matrix.Finally, it is difficult to prepare materials containing mica plateletsbecause excessive shear conditions may cause breakage of the platelets,which can ruin desired appearance.

The articles according to the present invention have a desirablemetallic flake appearance, yet they avoid the above-identified problemswith previous compositions having this same appearance.

SUMMARY OF THE INVENTION

The transparent articles disclosed herein have a metallic flakeappearance. These articles are formed by dispersing an amount of metaloxide-coated glass platelets in a transparent thermoplastic matrix. Theamount and size of platelets must be sufficient to create the metallicflake appearance, but not so high that the article appears opaque andmetallic. The matrix must be transparent because the platelets haveminimal affect on the appearance of opaque materials.

The method for making a transparent article disclosed herein comprisesmelt extruding a transparent polymer matrix together with an amount ofmetal oxide-coated glass platelets effective to provide a metallic flakeappearance. It is important in this process to avoid excess shearbecause such treatment can cause physical damage to the platelets, whichresults in a chemical interaction that causes the transparent matrix toyellow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term “article” designates any and all items madefrom a thermoplastic, including thermoplastic compositions prior tomolding (e.g., pellets) and molded, extruded, laminated, cast orotherwise processed items. Where the term articles designates pellets,the pellets may themselves have a rough surface, and therefore may notlook transparent, but will be capable of forming transparent articlesupon processing. Such pellets should still be considered to betransparent, as defined below.

As used herein, the term “transparent” means a transparent, natural ortranslucent article having a light transmittance above 50%. Thetransmittance is measured according to ASTM procedure D1003, using a BYKGardner Hazeguard Plus instrument. The machine operates by measuring theintensity difference between the projected light and the transmittedlight using a photodetector. A transparent article according to thisdefinition may have reduced transmission, due to the inclusion of someother ingredients (e.g., dyes) but will still have light transmittanceabove 50%.

As used herein, the term “natural” refers to an article having a lighttransmittance above 80%. Such materials may actually contain smallamounts of dyes designed to offset any other color which may be anundesirable artifact of the manufacturing process (e.g., yellowing), orto provide a specific color in combination with the metallic look.

The finished articles according to the invention have adequatetransparency to produce the metallic flake appearance.

The transparent thermoplastic matrix described above may be anytransparent thermoplastic material that is compatible with metaloxide-coated glass platelets. Suitable transparent thermoplasticmaterials include, but are not limited to polycarbonates, copolyestercarbonates, polymethyl methacrylate, polyetherimides, transparentpolyimides, halo olefin polymers, transparent polyamides (nylons),polyesters, transparent polycarbonate-polyester blends, polysulfones,polyether and polyphenyl sulfones, transparent acrylonitrile butadienestyrene, styrene acrylonitrile (SAN), polystyrene, cellulosics, miscibletransparent polystyrene-polyphenylene oxide (PS-PPO) blends, acrylics,polycarbonate-polysiloxanes, polyetherimide-polysiloxanes, polyarylates,polyethylene terephthalate, and blends and copolymers of all of theabove. More preferred transparent thermoplastic matrix materials arepolyetherimides, polymethyl methacrylate, polycarbonate (homopolymer orcopolymers), copolyester carbonates, polyethylene terephthalate (PET),styrene acrylonitrile, polystyrene, transparent acrylonitrile butadienestyrene and cellulosics. An even more preferred matrix material is aclear aromatic polycarbonate homopolymer based primarily on thebisphenol-A monomer. A most preferred embodiment of the invention is acopolyester carbonate made by reacting a dicarboxylic acid (e.g.,dodecanedioic acid) with bisphenol-A monomer. Various methods forsynthesizing these materials are well known in the art. For example,U.S. Pat. No. 5,364,926 describes the melt process for makingpolycarbonate, and is incorporated by reference herein. Moreover, theinterfacial, melt and solid state methods for making polycarbonate aregenerally summarized in the Encyclopedia of Polymer Science andEngineering, John Wiley & Sons, Vol. 11, pp. 651-655 (1988).

Metal oxide-coated glass platelets are preferably made by firststretching a molten C glass into thin sheets, beads or glass tubesfollowed by crushing this glass into flakes. C glass is a form of glassthat is resistant to corrosion by acid and moisture due to its zincoxide content. Typically, these glass flakes are coated by dispersingthem in water at a concentration of 10 to 20%. Next, an appropriate ironor titanium source is added while maintaining the pH at an appropriatelevel (e.g., by adding a base) to cause precipitation of hydroustitanium dioxide or hydrous iron oxide on the glass flake. Then an acidis typically added, the flakes are washed and subsequently calcined.Suitable metal oxide-coated glass platelets and methods for making themare described in U.S. Pat. No. 5,753,371, which is hereby incorporatedby reference.

It is preferred to use platelet loadings of 0.005 to 5 percent by weightof the transparent polymer matrix. It is more preferred to use plateletloadings of 0.01 to 2 percent by weight. If the loading is too low, themetallic flake appearance will not be observable. If the loading is toohigh, the entire article will seem metallic, will not be transparent,and will have degraded physical properties (e.g., poor impactperformance). The average particle size of the glass platelets istypically from 30 to 200 microns.

The transparent matrix may optionally further contain an opticalbrightening agent, a dye or dyes (which may be fluorescent), a lightdiffuser, stabilizers and/or antioxidants, pigments, antistatic agents,mold release agents and ultraviolet light (“UV”) stabilizers. None ofthese additives should exceed an amount which will cause the matrix tobecome opaque.

Suitable optical brightening agents include, but are not limited to,aromatic stilbene derivatives, aromatic benzoxazole derivatives, oraromatic stilbene benzoxazole derivatives.

Any type of dye may be added which is compatible with the matrix anddoes not cause the matrix to become opaque. Examples of some fluorescentdyestuffs include Permanent Pink R (Color Index Pigment Red 181, fromClariant Corporation), Hostasol Red 5B (Color Index #73300, CAS#522-75-8, from Clariant Corporation) and Macrolex Fluorescent Yellow10GN (Color Index Solvent Yellow 160:1, from Bayer Corporation).

It may be desirable to add a light diffuser to the transparent polymermatrix. Adding a light diffuser will create a translucent matrix.Suitable light diffusers include, but are not limited to,polytetrafluoroethylene, zinc oxide, and polymethylmethacrylate. Forexample, Techpolymer MBX-series crosslinked polymethylmethacrylatemicrospheres, which are available in various diameters from NagaseAmerica (e.g., 5-50 micron avg. diameter), may be added to the matrix.

It may also be advantageous to add stabilizers and antioxidants to thetransparent thermoplastic matrix. Some examples of suitable stabilizersand antioxidants include phosphites (e.g., aromatic phosphite thermalstabilizers), metal salts of phosphoric and phosphorous acid, hinderedphenol antioxidants, epoxides, aromatic lactone radical scavengers, andcombinations thereof.

Any other type of pigment that is well known for inclusion inthermoplastic materials can also be added to the transparent polymermatrix, provided the amount of pigment added is sufficiently low topreserve transparency and metallic flake appearance of the article.Suitable pigments include titanium dioxide, zinc sulfide, carbon black,cobalt chromate, cobalt titanate, cadmium sulfides, iron oxide, sodiumaluminum sulfosilicate, sodium sulfosilicate, chrome antimony titaniumrutile, nickel antimony titanium rutile, and zinc oxide.

Suitable antistatic agents include, but are not limited to, phosphoniumsalts, polyalkylene glycols, sulfonium salts and alkyl and aryl ammoniumsalts.

Suitable mold release agents include, but are not limited to,pentaerythritol tetracarboxylate, glycerol monocarboxylate, glyceroltriscarboxylate, polyolefins, alkyl waxes and amides.

Suitable UV stabilizers include, but are not limited to, substitutedbenzotriazoles, or triazines, or tetraalkylpiperidines. The UVstabilizers may be mixed into the thermoplastic matrix, or they can beincluded only in a “hardcoat” transparent protective layer which isapplied over the viewing surface, or stabilizers can be included both inthe matrix and the hardcoat.

The matrix may further comprise other resins and additives such as heatresisting agents, anti-weathering agents, lubricants, plasticizers,flame retardants, and flow-improving agents. Again, the transparency andthe metallic flake appearance of the matrix are limiting factors inadding any of these materials. These additives may be introduced in amixing or molding process.

To prepare the resin composition of the invention, the components may bemixed by any known methods. Typically, there are two distinct mixingsteps: a premixing step and a melt mixing step. In the premixing step,the dry ingredients are mixed together. This premixing step is typicallyperformed using a tumbler mixer or a ribbon blender. However, ifdesired, the premix may be manufactured using a high shear mixer such asa Henschel mixer or similar high intensity device. The premixing stepmust be followed by a melt mixing step where the premix is melted andmixed again as a melt.

Alternatively, it is possible to skip the premixing step, and simply addthe raw materials directly into the feed section of a melt mixing devicevia separate feed systems. In the melt mixing step, the ingredients aretypically melt kneaded in a single screw or twin screw extruder, aBanbury mixer, a two roll mill, or similar device.

It is preferred to skip the premixing step and introduce the plateletsinto the molten polymeric matrix downstream in an extruder after thepoint where the polymer melts. This process works better than feedingthe platelets at room temperature into the mouth of the extruder.Feeding at room temperature is problematic because mixing the solidpolymer matrix with the platelets and subsequently melting the polymerin an extruder subjects the platelets to high shearing forces, whichtends to cause breakage of the platelets. It is undesirable to breakapart the platelets because they may become too small to achieve thedesired metallic flake appearance. Moreover, the broken platelets mayundergo a chemical reaction with the matrix, which causes yellowing ofthe matrix. Feeding into the melt is also preferred because it helpseliminate dust problems associated with adding dry platelets to themouth of the extruder.

In an alternate, preferred embodiment of the invention, the preferredmethod described above can be used to form “concentrate” pelletscomprising platelets dispersed in the matrix wherein at a higherconcentration than the finished pellets. These “concentrate” pellets arethen fed into the feed section of a single or twin screw extrudertogether with additional matrix material (pellets or flake) to formfinished pellets having a diluted concentration of the platelets.Alternatively, the concentrate pellets can be added to the extruder at aposition down stream from the feed section.

The concentrate method eliminates the potential of contaminating nearbyprocesses with raw glass flake. Also, the additional matrix material fedtogether with the concentrate pellets may be different from the matrixmaterial in the concentrate pellets. However, the additional matrixmaterial must be miscible with the matrix material used for theconcentrate pellets such that the final pellets will be transparent.

Finished articles according to present invention may then bemanufactured by molding the melt mixed material into various shapesusing an injection molding machine or other known apparatus.Alternatively, a film can be formed on a substrate for example, byinsert molding, in-mold decorating, laminating, co-injection orco-extrusion. Additionally, a film can be extruded onto sheet or anotherfilm, which can then be thermoformed, vacuum-formed, or shaped in somemanner. All other known methods for creating multi-layer, or any otherarticles are also suitable.

The present invention is further described by way of the followingexamples. These examples are intended to be representative of theinvention, and are not in any way intended to limit its scope.

EXAMPLE 1

A formulation consisting of 5 kg of a copolyester carbonate having aMelt Flow index of 11 (300C, 1.2 kg, ASTM D1238) was prepared byreacting dodecanedioic acid with bisphenol A and phosgene, as describedin U.S. Pat. No. 5,025,081, which is incorporated by reference herein.Next, the 5 kg of resin powder, 13.5 g of mold release agent(pentaerythritol tetrastearate), and 3 g of tris (2,4-di-t-butylphenyl)phosphite were added to a container. 20 g of TiO2 coated glass flake,known commercially as Firemist Pearl sold by Engelhard Corporation, wasadded to this container. The container was sealed and mixed by shakingit in a paint shaker. The blended mixture was then compounded on a 2.5inch single screw extruder and cut into pellets. After 4 hours drying at220° F., the pellets were molded into various test specimens.

EXAMPLE 2

A formulation consisting of 5 kg of a polycarbonate having a Melt flowindex of 14 was prepared by reacting bisphenol A with phosgene using theinterfacial method. The resin, 13.5 g of mold release agent(pentaerythritol tetrastearate), and 3g of thermal stabilizer (tris(2,4-di-t-butylphenyl) phosphite) were mixed together with 20g of TiO₂coated glass flake material, and pellets were prepared as described inExample 1.

EXAMPLE 3

A formulation was prepared as described in Example 2, with the exceptionthat only 5 g of TiO₂ coated glass flake was added.

EXAMPLE 4

A formulation was prepared as described in Example 1, with the exceptionthat only 5 g of TiO₂ coated glass flake was added.

COMPARATIVE EXAMPLE 5

A formulation was prepared as described in Example 1 with the exceptionthat 20 g of pearlescent mica material, known commercially as Magnapearl4000 sold by Engelhard Corporation, was added in place of the glassflake. Table I, below, shows a comparison of the properties observedupon measuring samples prepared in Examples 1-4 and in this comparativeexample.

TABLE I Notched Notched % Trans- Ex # izod (RT*) izod (0 C.) missionClarity Appearance 1 13 6.9 72.8 80.7 bright reflecting distinct flakesin polymer matrix. 2 3.1 — — — same as #1 3 12.6 2.9 — — same as #1 413.5 13.4  86.5 95.3 same as #1 5 2.7 — 38.0 59.8 Hazy, milkytranslucent *RT = room temperature

One can draw the several conclusions from the observed data. First, acomparison of Example 1 and 5 shows that mica imparts a different lookto the article and adversely affects impact strength. Second, thedeterioration in impact strength is a function of the loading of theTiO₂ coated glass flake. Third, the materials having a copolyestercarbonate matrix perform are much more tolerant of high loadings ofglass flake than polycarbonate homopolymers.

COMPARATIVE EXAMPLE 6

TiO₂ coated glass flake material was pulverized with a mortar and pestleand added to the ingredients in the manner of Example 1. The moldedmaterial made using the pulverized material was more yellow than that ofExample 1. Specifically, the yellowness index (hereinafter “YI”) (ASTMD1925) of the material with crushed flake showed a YI measurement 0.6greater than the uncrushed flake. Also, the flakes in the polymer matrixhad a duller appearance.

COMPARATIVE EXAMPLE 7

TiO₂ coated glass flake material was added, along with 100 g of titaniumdioxide in the manner of Example 1 in order to produce an opaque whitematerial. The presence of the flakes in the molded material was barelydiscernable visually.

COMPARATIVE EXAMPLES 8 AND 9

Two opaque samples, with and without TiO₂ coated flake, were prepared bymixing ingredients as summarized in Table II, below:

TABLE II Material Comparative 8 Comparative 9 BPA Polycarbonate Power3,000 g.   3,000 g.   Irgafos 168 1.8 g.  1.8 g.  EP97079 White GlassFlake 30 g. — Magna pearl 4000 — 30 g. Carbon Black 30 g. 30 g.

In Table II, the bisphenol A (BPA) polycarbonate powder was prepared bythe interfacial process. the Irgafos 168 is a phosphite stabilizerhaving the following chemical formula: tris-2,4di-t-butylphenylphosphite. The EP 97079 white glass flake (“FiremistPearl”) is commercially available from Englehard. As mentionedpreviously, Magna pearl 4000 is a mica flake material which is alsoavailable from Englehard.

The room temperature notched izod tests showed that Comparative Example2 had a value of 7.3, whereas Example 9 had a notched izod value of 3.9.

Because of the inclusion of carbon black, both of these formulationswere opaque, and did not have a metallic flake appearance.

What is claimed is:
 1. A transparent article having a metallic flakeappearance, which article comprises an amount of metal oxide-coatedglass platelets effective to provide a metallic flake appearance,wherein said platelets are dispersed within a transparent polymermatrix.
 2. The transparent article according to claim 1, wherein thetransparent polymer matrix further contains a dye or pigment.
 3. Thetransparent article according to claim 1, wherein the transparentpolymer matrix is natural.
 4. The transparent article according to claim1, wherein the transparent polymer matrix is polycarbonate withdispersed spheres of polymethyl methacrylate.
 5. The transparent articleaccording to claim 1, wherein the platelets are present in an amount of0.01 to 2 percent by weight.
 6. The transparent article according toclaim 5, wherein the transparent polymer matrix is selected from thegroup consisting of polycarbonate homopolymers, polycarbonatecopolymers, copolyester carbonates, polymethyl methacrylate,polyetherimides, transparent polyimides, halo olefin polymers,transparent polyamides, polyesters, transparent polycarbonate-polyesterblends, polysulfones, polyether and polyphenyl sulfones, transparentacrylonitrile butadiene styrene, styrene acrylonitrile, polystyrene,cellulosics, miscible transparent polystyrene-polyphenylene oxide(PS-PPO) blends, acrylics, polycarbonate-polysiloxanes,polyetherimide-polysiloxanes, polyarylates, polyethylene terephthalate,and blends and copolymers of all of the above.
 7. The transparentarticle according to claim 6, wherein the transparent polymer matrix isselected from the group consisting of polymethyl methacrylate,polycarbonate homopolymers, polycarbonate copolymers, copolyestercarbonates, polyethylene terephthalate, styrene acrylonitrilepolystyrene, transparent acrylonitrile butadiene styrene andcellulosics.
 8. The transparent article according to claim 7, whereinthe transparent polymer matrix comprises a polycarbonate homopolymer. 9.The transparent article according to claim 7, wherein the transparentpolymer matrix comprises copolyester carbonate.
 10. The transparentarticle according to claim 7, wherein the transparent polymer matrixconsists essentially of a polycarbonate homopolymer and copolyestercarbonate.
 11. The transparent article according to claim 1, wherein theplatelets have an average particle size of greater than 30 microns. 12.A method for making a transparent article which comprises melt extrudinga transparent polymer matrix together with an amount of metaloxide-coated glass platelets effective to provide a metallic flakeappearance, thereby dispersing the metal oxide-coated glass plateletswithin a transparent polymer matrix.
 13. The method according to claim12, wherein the transparent polymer matrix comprises a polymer selectedfrom the group consisting of a polycarbonate homopolymer and copolyestercarbonate.
 14. The method according to claim 13, wherein the meltextrusion is performed under conditions which avoid exposing theplatelets to sufficient shear to increase in the yellowness index of thetransparent article.
 15. The method according to claim 14, wherein theplatelets are introduced into molten polymer matrix downstream in anextruder.
 16. The method according to claim 15, wherein a concentrate ofhigh platelet content pellets are introduced into an extruder togetherwith an additional matrix material which does not contain the platelets.17. The method according to claim 16, wherein the matrix of theconcentrate pellets differs from the additional matrix material.
 18. Atransparent article having a metallic flake appearance, wherein saidarticle is prepared by melt extruding a transparent polymer matrixtogether with an amount of metal oxide-coated glass platelets effectiveto provide a metallic flake appearance, thereby dispersing the metaloxide-coated glass platelets within a transparent polymer matrix.